Runs 15 minutes then dies and won't start

[NROTOXIN]

Check AC output....

[davids2toys]

Originally Posted by Tom Wells

David,

There are web sites that give locations for buying alcohol-free gasoline. Here's one:

https://www.pure-gas.org/

If you look in CT you can find a list of 32 gas stations that are supposed to have it available.

Hope this helps,

Tom

Stewart's sells 91 Octane non ethanol in some of its VT and NY stores for 4.05 a gal.I am going up to Arlington VT over Christmas. They have a Stewart's there and I confirmed they sell it. This is a better option than making a special trip driving a 3 hour round trip to NY which would be the closest location to me

[davids2toys]

Now that I am looking at the fuel system lines I am a little concerned even though I never had a problem until this. Could be the ethanol in the gas. My fuel log and lines are not protect at all by the Turkey pan. See pics

[davids2toys]

No pics! I am getting an error message but not telling me what to do. So frustrating

[davids2toys]

Different browser attempt,
This worked but still one of the pics failed

[davids2toys]

One more showing the log

[davids2toys]

Deleted

[davids2toys]

Originally Posted by rnkjr

Chat GPT: Most Probable Causes (ranked)
1. MSD 6AL box failing when hot
Why this fits perfectly:

Car runs normally until fully heat-soaked (15–20 minutes).

Engine dies instantly, as if key was turned off — classic MSD box shutdown symptom.

After cooling 20–45 minutes it restarts immediately.

Numerous coils tried → no change.

Pickup tests OK cold and hot.

Grounds check OK.

Ignition switch replaced with no improvement.

Important detail:

MSD boxes often fail only when hot, and about 70% of the time they still pass the "paper clip test" when tested immediately after failure, especially if they are in the shade or starting to cool.

Even when they pass the paper clip test, the internal capacitors or the switching transistor can break down under heat + load.

2. Magnetic pickup intermittent when hot (despite 674 Ω)

Even though resistance is correct (MSD wants 500–700 Ω), failing pickups often:

test perfect cold,

test perfect immediately after a shutdown,

but fail only under thermal expansion + vibration.

This can produce the “dies instantly at a stop sign” symptom.

Testing tip:
Check AC voltage output while cranking during a hot no-start. You should see 0.3–1.0 volts AC.
If it drops to 0–0.1, the pickup is dying even if resistance is normal.

3. Heat-soak failure of the coil trigger signal path

You already tried multiple coils — that strongly suggests the coil is not the problem, but the trigger path TO the coil might be intermittent.

This includes:

MSD box to coil wire (heavy red + heavy orange)

MSD box ground path

Small red wire (switched 12V) heat drop / intermittent open

Loose spade connectors at the box

A small-red-wire voltage drop is a known MSD shutdown cause.

Well the first part of this certainly sounds like my issue. The pickup was put in a few years ago but has had hardly any use. Also looks perfect. When I called MSD the assured me if it passed the paper clip test it is DEFINATELY not the box!
So how do I do this AC voltage test? Where am I doing this test? What is the voltage drop/ heat drop at the small red wire, I don't understand. So what am I looking for at all the other locations you listed. I only have one spade terminal (yellow wire), it is on tightly

[rnkjr]

I hope you noticed, my prior post was a Chat GPT response to your first post. With that being said, here is the Chat GPT response to your 11:51PM post: 1. How to do the AC voltage test on the distributor pickup

Your MSD distributor has a magnetic pickup, which produces a small AC signal that tells the MSD box when to fire the coil.

Where to test:
Unplug the two-wire magnetic pickup connector going into the MSD box.
It’s the violet and green wires.

How to test:

Set your multimeter to AC volts (not DC).

Put the meter leads on the violet and green wires.

Have someone crank the engine.

What you should see:

0.3 to 1.0 volts AC while cranking = pickup is good

0.0 to 0.2 volts AC = pickup is failing even if the ohms reading was normal

Heat can kill the signal even though resistance checks fine — that’s why this test matters.

2. What “voltage drop at the small red wire” means

The MSD 6AL has two power feeds:

Big Red = main battery power

Small Red = switched ignition power (what wakes the MSD box up)

If the small red wire loses voltage when hot, the MSD shuts off instantly, just like turning off the key.

Where to test:
Back-probe the small red wire at the MSD 6AL box (the small plug).

How to test:

Set meter to DC volts.

Put black lead to a good ground.

Touch red lead to the small red wire.

Check reading while cranking during the hot no-start.

What you should see:

11.5–12.5 volts = normal

Anything 10.5 volts or lower = MSD won’t fire

Voltage jumping, flickering, or dropping sharply = bad ignition feed or switch connector

This is a very common cause of random MSD shutdowns.

3. What to look for at the other connections
A. Big Red (main power)

Should have 12–12.6V key ON and 10.5+ volts while cranking.

B. Big Black (ground)

Should be bolted to clean metal, preferably the engine block or battery ground.
If in doubt, run a jumper cable temporarily from the MSD ground to the battery negative and see if the problem disappears.

C. Orange & Black at the Coil

You don’t need to measure voltage here yet — just confirm the connectors are tight and not corroded.

D. Yellow spade connector

If you only have one yellow spade, that’s normally the tach output.
If it’s tight, leave it alone — it doesn’t affect starting unless it’s grounding out.

The real goal of these tests

You already replaced coils, ignition switch, checked grounds, and the pickup ohms fine. The next step is to catch the system in the act when it’s hot and refusing to start.

One of these readings will be wrong only during the failure window, and that will tell you whether it’s:

the pickup signal disappearing

the small red ignition feed dropping voltage

or the MSD box itself breaking down from heat

[Whodeeny]

I believe I had a failure similar to what you are experiencing. The car would start and run for a few minutes then die. I couldn't get it restarted immediately. If I waited until the next day it would restart then the same thing would happen. I initially thought the fuel filter was plugging up or I had bad gas. Finally it started, died then I couldn't get it restarted at all. I had it towed to a shop that works with restorations and special interest cars. They diagnosed a failed MSD box. A new box was installed and now the car starts and runs fine. HERE IS THE KICKER - I SENT THE BOX TO MSD FOR REPAIR. THEY CHECKED IT TOLD ME THERE IS NOTHING WRONG WITH IT. I will try the old MSD box again on the car in the spring when I am home again.
BD

[scott cooper]

I have been involved in a similar issue and we found a bad circuit breaker close to the fuel pump, small silver rectangle breaker that turned out to be bad, would be fine for a few minutes then would shut down and with no volts going to the pump car shut down, just a suggestion, thought for sure it was a bad fuel pump but not the case

[strictlypersonl]

Scott's idea is worth checking.
When the circuit breaker trips, everything should be dead. Easy to confirm when the fuel gauge doesn't respond to the ignition switch "on". Signal lights won't work either.

Circuit breaker bad: you can temporarily connect its wires together.

[davids2toys]

Originally Posted by rnkjr

I hope you noticed, my prior post was a Chat GPT response to your first post. With that being said, here is the Chat GPT response to your 11:51PM post: 1. How to do the AC voltage test on the distributor pickup

Your MSD distributor has a magnetic pickup, which produces a small AC signal that tells the MSD box when to fire the coil.

Where to test:
Unplug the two-wire magnetic pickup connector going into the MSD box.
It’s the violet and green wires.

How to test:

Set your multimeter to AC volts (not DC).

Put the meter leads on the violet and green wires.

Have someone crank the engine.

What you should see:

0.3 to 1.0 volts AC while cranking = pickup is good

0.0 to 0.2 volts AC = pickup is failing even if the ohms reading was normal

Heat can kill the signal even though resistance checks fine — that’s why this test matters.

2. What “voltage drop at the small red wire” means

The MSD 6AL has two power feeds:

Big Red = main battery power

Small Red = switched ignition power (what wakes the MSD box up)

If the small red wire loses voltage when hot, the MSD shuts off instantly, just like turning off the key.

Where to test:
Back-probe the small red wire at the MSD 6AL box (the small plug).

How to test:

Set meter to DC volts.

Put black lead to a good ground.

Touch red lead to the small red wire.

Check reading while cranking during the hot no-start.

What you should see:

11.5–12.5 volts = normal

Anything 10.5 volts or lower = MSD won’t fire

Voltage jumping, flickering, or dropping sharply = bad ignition feed or switch connector

This is a very common cause of random MSD shutdowns.

3. What to look for at the other connections
A. Big Red (main power)

Should have 12–12.6V key ON and 10.5+ volts while cranking.

B. Big Black (ground)

Should be bolted to clean metal, preferably the engine block or battery ground.
If in doubt, run a jumper cable temporarily from the MSD ground to the battery negative and see if the problem disappears.

C. Orange & Black at the Coil

You don’t need to measure voltage here yet — just confirm the connectors are tight and not corroded.

D. Yellow spade connector

If you only have one yellow spade, that’s normally the tach output.
If it’s tight, leave it alone — it doesn’t affect starting unless it’s grounding out.

The real goal of these tests

You already replaced coils, ignition switch, checked grounds, and the pickup ohms fine. The next step is to catch the system in the act when it’s hot and refusing to start.

One of these readings will be wrong only during the failure window, and that will tell you whether it’s:

the pickup signal disappearing

the small red ignition feed dropping voltage

or the MSD box itself breaking down from heat

Wow, great explanation...THANKS. real busy at the moment and going away twice before the end of the month. I will try to get to some of this if I can. also, one thing I forgot to mention, My MSD box is in the cockpit, not the engine compartment so the heat soak in the engine bay should not be a factor affecting the box directly

[davids2toys]

Originally Posted by strictlypersonl

Scott's idea is worth checking.
When the circuit breaker trips, everything should be dead. Easy to confirm when the fuel gauge doesn't respond to the ignition switch "on". Signal lights won't work either.

Circuit breaker bad: you can temporarily connect its wires together.

Scott and Bob: I have a mechanical fuel pump

[Tom Wells]

David,

Happy New Year!

Did you get the chance to try the no-alcohol fuel?

Tom

[davids2toys]

Hi Tom,
I went to VT the end of Dec. I brought along two 5 gallon gas cans. I filled them with premium 91 octane non ethanol gas. Still sitting on the floor in back of the Cobra. I have not been able to do anything on the car due the weather and my garage in Winter configuration with snowblowers, shovels, plow truck, etc, etc. I also will need to get the present gas level down to the pick up so I will have minimum dilution of the new non ethanol gas. Right now I have about 1/4 tank of 93 octane ethanol fuel.If I drain the tank I will be way below the pickup level which the require a ton of gas just to regain the prime. When I first got the car I was running out of gas so I was heading to the nearest gas station about 4 miles down the road. The gauge was reading E. All of a sudden the car started exhibiting all the symptoms of fuel starvation. I started weaving back and forth to keep the fuel going in the pickup.Made it about a mile like this and then it finally died.Big mistake because it took many hitchhiking trips to the gas station and filling a 1 gallon anti freeze which they had lying around.I think it took about 4 gallons before the gas level came up before it would start. Will never do that again. If anybody ends up in this situation, dont try to keep the car alive unless you can actually see the gas station!!! Now I always fill up around the 1/4 mark.

[mrmustang]

Originally Posted by davids2toys

Hi Tom,
I went to VT the end of Dec. I brought along two 5 gallon gas cans. I filled them with premium 91 octane non ethanol gas. Still sitting on the floor in back of the Cobra. I have not been able to do anything on the car due the weather and my garage in Winter configuration with snowblowers, shovels, plow truck, etc, etc. I also will need to get the present gas level down to the pick up so I will have minimum dilution of the new non ethanol gas. Right now I have about 1/4 tank of 93 octane ethanol fuel.If I drain the tank I will be way below the pickup level which the require a ton of gas just to regain the prime. When I first got the car I was running out of gas so I was heading to the nearest gas station about 4 miles down the road. The gauge was reading E. All of a sudden the car started exhibiting all the symptoms of fuel starvation. I started weaving back and forth to keep the fuel going in the pickup.Made it about a mile like this and then it finally died.Big mistake because it took many hitchhiking trips to the gas station and filling a 1 gallon anti freeze which they had lying around.I think it took about 4 gallons before the gas level came up before it would start. Will never do that again. If anybody ends up in this situation, dont try to keep the car alive unless you can actually see the gas station!!! Now I always fill up around the 1/4 mark.

So are you saying you ran out of gas and that was the cause of the car not running for more than a few minutes?

[Tom Wells]

David,

Understood! Been there....

We'll do a dance for good weather so you can see if it changes anything ;-)

Tom

[davids2toys]

Originally Posted by mrmustang

So are you saying you ran out of gas and that was the cause of the car not running for more than a few minutes?

NO, I said in the post when I first got the car. That was over 10 years ago. I was giving the reason why now I want to get the fuel level as low as possible before adding the non ethanol gas

[mrmustang]

Originally Posted by davids2toys

NO, I said in the post when I first got the car. That was over 10 years ago. I was giving the reason why now I want to get the fuel level as low as possible before adding the non ethanol gas

Honestly, if you are adding 10 gallons to a tank that is currently 1/4 full, you have diluted the ethanol based fuel farther than you would need to be concerned about.
If you have concerns about ethanol, then rebuilding your fuel pump and carburetor, along with replacing your fuel filter (do you have more than one?) would need to be accomplished beforehand. In addition, pulling your fuel pickup out of the tank and checking and more than likely replacing the sock would also be high on my to do list.


Bill S.